B12 â an essential vitamin for land-dwelling animals including humans – also turns out to be an essential ingredient for growing marine plants that are critical to the ocean food web and Earthâs climate, scientists have found. The presence or absence of B12 in the ocean plays a vital and previously overlooked role in determining where, how much and what kinds of microscopic algae, or phytoplankton, will bloom in the sea. These photosynthesizing plants in turn, have a critical impact on Earthâs climate. They draw huge amounts of carbon dioxide from the air, incorporating carbon into their bodies. When they die or are eaten, carbon is transferred to the ocean depths, where in cannot re-enter the atmosphere.